1. Field of the Invention
This invention relates to electrical devices comprising conductive polymer compositions and to circuits comprising such devices.
2. Introduction to the Invention
Electrical devices comprising conductive polymer compositions are well-known. Such devices comprise an element composed of a conductive polymer. The element is physically and electrically connected to at least one electrode suitable for attachment to a source of electrical power. Those factors determining the type of electrode used include the specific application, the configuration of the device, the surface to which the device is to be attached, and the nature of the conductive polymer. Among those types of electrodes which have been used are solid and stranded wires, metal foils, perforated and expanded metal sheets, and conductive inks and paints. When the conductive polymer element is in the form of a sheet or laminar element, metal foil electrodes which are directly attached to the surface of the conductive polymer, sandwiching the element, are particularly preferred. Examples of such devices are found in U.S. Pat. Nos. 4,426,633 (Taylor), 4,689,475 (Matthiesen), 4,800,253 (Kleiner et al), 4,857,880 (Au et al), 4,907,340 (Fang et al), and 4,924,074 (Fang et al), the disclosures of which are incorporated herein by reference.
As disclosed in U.S. Pat. Nos. 4,689,475 (Matthiesen) and 4,800,253 (Kleiner et al), microrough metal foils having certain characteristics give excellent results when used as electrodes in contact with conductive polymers. Thus U.S. Pat. No. 4,689,475 discloses the use of metal foilswhich have surface irregularities, e.g. nodules, which protrude from the surface by 0.1 to 100 microns and have at least one dimension parallel to the surface which is at most 100 microns, and U.S. Pat. No. 4,800,253 discloses the use of metal foils with a microrough surface which comprises macronodules which themselves comprise micronodules. Other documents which disclose the use of metal foils having rough surfaces, but which do not disclose the characteristics of the foils disclosed in U.S. Pat. Nos. 4,689,475 and 4,800,253, are Japanese Patent Kokai No. 62-113402 (Murata, 1987), Japanese Patent Kokoku H4-18681 (Idemitsu Kosan, 1992), and German Patent Application No. 3707494A (Nippon Mektron Ltd). The disclosure of each of these U.S., Japanese, and German documents is incorporated herein by reference.